CreateJS/PreloadJS — pull request #32 by KatsuomiK (2013-02-10 21:47:42+00:00)
Title: Add AAC to sound extensions

In HTML5 games, MPEG-4 AAC and Ogg Vorbis are preferred audio codecs so AAC support is needed.

Here is an article by the developer of Construct 2.
https://www.scirra.com/blog/64/why-you-shouldnt-use-mp3-in-your-html5-games